Fix for bug 936798. Allow a client to select which
region endpoint they want from the service catalogue.
The region can be set via the environment variable
OS_REGION_NAME or via the '-R/--region' command line
option.
If a single image endpoint is returned from keystone,
the client will use that even if no region was specified
(the default). Where multiple endpoints exist a region
must be provided.
Change-Id: I6797f8ddf88d5875caf194913082c3fe24c86585
8d46288e9c